High temperature heat treatment of metals



Aprxl 5, 1960 w. E. ENGELHARD HIGH TEMPERATURE HEAT TREATMENT OF METALSFiled March 17, 1958 2 Sheets-Sheet 1 di .'T p- ATTORNEY April 5, 1960w. E. ENGELHARD 2,931,636

HIGH TEMPERATURE HEAT TREATMENT oF METALS Filed March 17. 1958 2sheets-sheet 2' ATTORNEY man TEMPERATURE HEAT TREATMENT F METALS WilliamE. Engelhard, Apalachn, N.Y.

Application March 17, 1958, Serial No. 721,724 lz claims.v (cl. zes- 41)This invention relates to the heat treatment of metals at hightemperatures. One of the difficulties encountered in high temperatureheating of parts in furnaces .is that there is a tendency for theatmosphere to filter through to the parts being heat treated, formingoxides and impurities thereon. Substantial seepage of the atmosphereinto contact with the parts, frequently encountered in conventional hightemperature heat treatment procedures, called a high dew point is aserious shortcoming.

Pursuant to this invention, the parts may be safely heat treated in acasing made of relatively inexpensive metals such as iron, the partsbeing swept by hydrogen gas under pressure which then passes outwardlyand into the atmos-y phere so that the inner casing and the partstherein are maintained at all times in a gaseous bath which preventsseepage and flow of atmospheric air and maintains a low dew pointcondition in the casing containing the parts. Pursuant to the invention,the parts to be heat treated mayl thus be heated and brought to thedesired temperature without contamination.

Examples of practical devices embodying the invention` are describedbelow Vand in the accompanying drawings; the invention is not limitedthereto, but covers all other forms coming within the scope or purviewof the disclosure herein.

In the drawings:

Fig. 1 is a vertical longitudinal sectional, partly fragmentary view ofahigh temperature furnace for treating parts, embodying the invention,arrows showing the path of the gas sweeping the parts and thence passingover the outer-'wall of the inner casing and between said outer wall andthe inner wall of the enclosing rst casing and thence into theatmosphere,

Fig. 2 is a vertical sectional view thereof, taken at line 2-2 of Fig.1,

Fig. 3 is a partly fragmentary, elevational view, taken at line 3--3 ofFig. l,

Fig. 4 is a partly fragmentary view of a casing which may be used incarrying out the invention,

Fig. 5 is a fragmentary, sectional view of an inner casing used incarrying out the invention, and

Fig. 6 is a fragmentary, elevational view of a form of casings embodyingthe invention.

In Fig. 1 the invention is shown applied to a high temperature furnace10 having a rear wall 11, and longitudinally elongated wall means 12extending forwardly therefrom, in this instance comprising a top walland bottom and side walls, but, which may be rectangular, circular orany other desired or convenient form cross sectionally, defining anelongated recess 13 open at the front 14 of the furnace and defining anopen front face thereat. The furnace may be provided with electricheater elements 15 or any other desired or convenient source for heatingthe recess 13 and thereby heating the parts 16 positioned therein. Adoor 17 is adapted to be positioned against the open front 14 of thefurnace, to close the same as shown in Fig. 1. Door 17 may be providedwith a bracket 1 8 to which a cable 19 may be affixed for moving thedoor ji y ired States arent 'ige against and away from the front 14 ofthe furnace; counterbalance weights 20 may (Fig. 3) be secured tothecable 19 entrained over pulleys (not shown).

Pursuant to the invention, a novel chamber apparatus is provided forinsertion into the furnace recess 13 through the open front 14 of thefurnace for holding the work p casing 24, in this instance alsocomprising a top wall 25 and bottom and side walls all longitudinallyelongated, and a front end plate 26 rigidly secured thereto, as bywelding at 27, providing a gas tight seal. The wall means of the secondcasing is slightly shorter than the top, bot-V tom and side wall meansof the first casing so that (Figs. 4 and 6) said casings may be securedtogether with the front end of the irst casing secured to the end plate26 of the second casing, the side Walls of the casings then definingtherebetween a constricted, elongated passageway 32 (Fig. 1), the freeend 33 of the second casing 24 then defining with the rear wall of thefirst casing a passageway for gases passing through the second casing 24from a source 34 (presently described) and then through the elongatedpassageway 32, and, as noted by the arrows in Fig. l, between the door17 and front end 14 of the furnace 10 and to the atmosphere. The outercasing preferably is made of a heat resistant alloy, such as Nichrome orInconel, While the inner casing 24 may be made of iron.`

length 40 (Fig. l) substantially greater than its height 42- (Fig. 2)the casings 21, 24 being so proportioned that the space between the sidewalls ofthe casing, indicated by the arrows 43, Fig. 2, is a fraction ofthe height of the inner casing so that gas pumped under pressure throughthe pipe 34 and thence through the second casing 24 (arrows Fig. 1) willblanket the parts 16 therein and pass intermediate the open rear end ofsecond casing and the end of the first casing and thence at 32intermediate the casing side walls and through the front end 14 of thefurnace, rapidly discharging to the atmosphere and maintain ing a lowdew point in the inner casing 24 containing the parts being treated. Aslip coating 28 may (Fig. 5) be applied to the side wall member of thesecond casing 24 to prevent the work from adhering thereto.

In practice, the furnace 10 is preferably disposed horizontally as, forexample, indicated in Figs. 1 and 2 by the horizontal surface 44, andthe parts 16 are positioned in the second casing 24 and then the firstcasing 21 secured to the end plate 26 of the second casing, as forexample, by the use of bridge members such as shown in Fig. 6 at 45 andin Fig. 4 at 45', said bridge member being welded at opposite ends tothe end plate 26 of the second casing and to the first casing, with asubstantial portion of the bridge member extending therebetween (Fig. 6)or being formed as bolts passed through extensions or plates on the endplate 26 and first casing 21 (Fig. 4). The parts 16 are positioned inthe second casing and then the casings secured together and insertedinto the furnace recess 13;

the parts are maintained in the blanket of gas supplied through thesource 34, while being treated.

In the drawings (Fig. 1), the second casing is shown provided withprotuberances 46 at the bottom thereof which serve to space the bottomsof the first and second casings 21, 24 maintaining the constrictedelongated gas passageway 32 completely around the second casing 24. Theparts 16 and the outer face of the second casing 24 will be continuouslywashed with gas during the heating operation and any ambient gas whichsought to breathe through or permeate the casings would be swept out ofthe furnace by the gas from source 34 pumped into the second casing 24under pressure. The door 17 is positioned against the front end 14 ofthe furnace 10 as shown in Fig. l and, although in practice the fit maybe an accurate one, gas from source 34 sweeping over parts 16 and thencemore rapidly through the constricted space 32 between the casings willescape (arrows, Fig. 1-) between the front 14 of the furnace 10 and thedoor 17 and into the atmosphere.

After the parts have been heat treated to a sufficient degree in thefurnace, the casings may be withdrawn and the bridge members such as 45,45' cut to separate the casings. The bridge members 45, 4S may bedispensed with by otherwise connecting or directly welding the firstcasing to the second casing but the provision of bridge members or theirequivalent provides a convenient means for readily separating thecasings. If desired, a heat insulating gasket 47 may (Fig. 5 bepositioned on the inner face of the end plate 26 of the second casing.

If` in use the free end of the first casing becomes separated to anappreciable degree from the end plate 26 of` the second casing, a gasket48 (Fig. 6) may be stuffed between the front of the first casing and theend plate of the second casing. Gaskets 47, 48 may be made of anysuitable or desired material such as silicon carbide wool.

The door 17 may be provided with a recess 49 (Figs. 1v and 3) to permitthe door to be slid down over the pipe 34, or a two part door may beprovided to close around said pipe. The pipe 34 may be connected to asource 50 (Fig. 3) of another gas such as CO2, argon, nitrogen or otherdesired gas for flushing the interior of the second casing 24, connectedto the T 37 through a valve 51.

Having thus described my invention, what I claim as new and desire tosecure by Letters Patent is:

1. An elongated high temperature heat treating furnace to behorizontally positioned on a supporting surface in parallel relationthereto comprising a rear wall and longitudinally elongated wall meansextending forwardly therefrom, defining an elongated tubular recess in,and terminating in a free edge defining an open front face of, thefurnace, said recess extending from the open front face to the rear wallinteriorly thereof, an elongated first casing having an end wallslightly smaller than the furv nace wall in dimensions transverse to thefurnace, and first casing tubular wall means extending forwardlytherefrom and of less length than the furnace'recess, said first casingto be inserted into the furnace recess with the free end of its wallmeans substantially in the plane of the front face of the furnace, and asecond casing comprising an end plate as large as the open front face ofthe first casing and second casing tubular wall means secured to the endplate and of slightly less length and cross sectional dimensions thanthe first casing, the lower portion of said last-mentioned wall means tosupport the partsvto be heat treated in the furnace, the free edge ofthe first' casing being slightly spaced from and secured to the endplate of the second casing, a gas pipe secured to said end plate inregistry with an aperture provided in said plate, for passage of gasunder pressure into the second casing and thus over the parts thereinand through the restricted, long passage defined by the wall means ofthe casings and thence laterally past the front face of the furnace, adoor positioned against the front face of the furnace and against theend plate of the second casing, and slotted to clear the pipe and allowthe door to slidably move laterally relative to the front face of thefurnace.

2. In a furnace as set forth in claim 1, said first casing being made ofheat-resistant material, and a bridge member fixed to the end plate ofthe second casing and to the wall means of the lfirst casing adjacentthe free end thereof, holding said end plate andfirst casing in abuttingrelation.

References Cited in the file of` this patent UNITED STATES PATENTS446,947 Land Feb. 24, 1891 1,333,225 Stewart Mar. 9, 1920 1,997,680 DeCoriolis et al Apr. 16, 1935 2,124,764 Comstock July 26, 1938 2,480,293Hulme Aug. 30, 1949 2,744,745 Engelhard May 8, 1956 FOREIGN PATENTS666,965 Germany Feb. 24, 1891

